In the positive pressure breathing treatment of a patient a pulse of air is forced into the patient's lungs and with the termination of the pulse the patient exhales. To accomplish this, a breathing circuit is connected between the patient and a ventilator. The ventilator produces and times the pulses as well as conditions the air supplied to the patient, such conditioning primarily being a matter of increasing temperature and humidity of the air. The patient end of the breathing circuit is connected to an endotracheal or tracheostomy tube located in the patient. Since both of these tubes by-pass the patient's upper airway, it is necessary that the air being supplied to the patient be properly conditioned so as to provide to the lungs temperature and humidity levels comparable to that provided by the upper airway. It is customary for the ventilator to deliver air into the circuit saturated with water, and at a temperature such that by the time the air has passed through the circuit to the patient, with the resulting heat losses, it will be received by the patient at approximately body temperature. As the air moves through the circuit to the patient from the ventilator the reduction in air temperature reduces the quantity of moisture that the air can hold at one hundred percent relative humidity, and the excess moisture condenses out as liquid water. The term "air" is used herein to refer to the gas that is supplied to the patient for breathing purposes. That gas is not necessarily identical to the ambient atmosphere, since the percentages of oxygen, nitrogen, etc., may be adjusted or enriched to accommodate the requirements for the treatment of a particular patient.
Such condensate is troublesome. If allowed to collect it can reduce the effective cross-sectional area (lumen) of the inspiratory conduit available for transmitting air to the patient. The use of a condensate collection bottle on the inspiratory side is undesirable for a number of reasons which include: (a) it increases the compressible volume of the system necessitating an increase in the total volume of gas that the ventilator must deliver, which in turn adversely affects the determination of physiological parameters such as static and dynamic lung compliances; (b) the volume and weight of such a condensate container adds to the problems of bulk and creates a requirement for increased support of the ventilation circuit; (c) such a collection container can become a site for bacterial growth; and (d) emptying the collection bottle interrupts the ventilation of the patient. My prior U.S. Pat. Nos. 3,865,106 and 3,945,378 relate to ventilation circuits which incorporate the feature of placing the inspiratory conduit concentrically within the expiratory conduit to thereby reduce the heat loss of the inspiratory conduit to the end that less condensate will occur in the inspiratory conduit. While such arrangement can reduce the amount of condensate in the inspiratory conduit it does not eliminate it.
A principal object of the present invention is to provide a ventilation circuit between the patient and the ventilator which is effective in removing condensate from the inspiratory conduit without the disadvantages associated with a condensate bottle interposed directly in the inspiratory conduit, and without any deleterious effects on the normal operation of the ventilation circuit. Incidentally, the term "ventilator" is used herein to include all of the various types of apparatus for supplying the conditioned air and pulsing the circuit with positive pressure inhalation pulses separated by exhalation periods. Such devices are sometimes referred to as respirators, positive pressure machines, or volume ventilators, and the present invention is equally applicable thereto.
Another feature of the present invention is that the manifold through which the condensate removal takes place is at the ventilator end of the circuit and can in fact be supported directly by the ventilator. This, plus the fact that the exhalation valve which is pulsed by the ventilator is a part of that manifold, is quite advantageous. In contrast to this, conventional circuits will have the exhalation valve at some location about midway of the ventilation circuit. Since this generally is a fixed location and is a point requiring support because of the presence of the valve, it is a limiting factor in the physical accommodation of the circuit to the specific needs of the individual patient. The elimination of this limiting factor can be a great advantage in the ability of the medical personnel to accommodate the circuit to the needs of the patient, to the end of achieving the greatest patient comfort, etc. Furthermore, this change provided by the present invention permits the arrangement of both the inhalation and exhalation conduits in a manner such that the condensate in each will flow downhill throughout the lengths of the conduits to the ends connected to the ventilator mounted manifold.
As in the prior art devices, the inhalation and exhalation conduits communicate with each other and with the patient's endotracheal or tracheostomy tube at a fitting located close to the patient. In contrast to the prior art, however, in the present invention the other ends of the inhalation and exhalation conduits enter a manifold located immediately adjacent the ventilator. In this manifold there are separate inhalation (inspiratory) and exhalation (expiratory) chambers, the inhalation chamber being generally above the exhalation chamber. The air supply from the ventilator communicates with the inhalation chamber. The exhalation control valve is put in the lowermost part of the exhalation chamber, with a fluid discharge connection on the manifold, below that valve and communicating with the valve. A lowermost part of the dividing wall between the inhalation chamber and the exhalation chamber has an orifice therein. While the liquid condensate in the inhalation chamber will drain through this orifice into the exhalation chamber for ultimate discharge through the valve and the discharge connection, the airflow in the circuit to and from the patient is essentially unaffected by the existence of this orifice, i.e., for all practical purposes no airflow through the orifice occurs in the inspiratory or expiratory portions of the breathing cycle. This is due to the fact that during these portions of the breathing cycle the inspiratory and expiratory conduits are in communication with each other at the ends thereof adjacent the patient and because of this connection the air pressures in the two conduits, and thus in the two chambers in the manifold are essentially equal. Since the air pressure on each side of the orifice is essentially equal there is no significant air flow through the orifice. Thus the presence of the orifice fails to have any deleterious effect on the breathing cycle produced by the ventilator and the ventilation circuit. Since both the inspiratory and expiratory conduits may be arranged to drain downhill to the manifold, the condensate which develops in each will drain into the manifold and, during the times that the exhalation valve is open, will pass through that valve to the discharge connection on the manifold. A collection container or bottle is connected to this discharge connection to receive such condensate and other liquid from the system. When full, it may be disconnected and emptied without in any way interfering with the positive pressure ventilation of the patient.
Other features of the invention will be apparent from the following description as well as the role played thereby in providing a ventilation circuit apparatus which is easily accommodated to meet the needs in the treatment of a patient under the individual circumstances present in that patient's treatment.